For the purpose of road safety and traffic efficiency, vehicular networks will primarily operate in the 5.9 GHz frequency band. By regulation, this spectrum is split into several wireless channels of 10 MHz bandwidth. In order to efficiently utilize the spectrum, vehicles need to operate on multiple channels simultaneously, also referred to as multi-channel operation (MCO). IEEE 1609.4 (for reference, see IEEE, IEEE 1609.4-2010—IEEE Trial-Use Standard for Wireless Access in Vehicular Environments (WAVE)—Multi-Channel Operation, IEEE Std., 2010) is a standard for MCO for the IEEE 1609 protocol stack. It relies on channel switching or alternating between a Control Channel (CCH) and Service Channels (SCHs) for single-radio transceivers, and between SCH for dual-radio transceivers; the latter when considering that one radio is constantly tuned in the CCH. However, in addition to not considering the application relevance, this time division oriented channel switching approach was shown to be inefficient in channel utilization (for reference, see Chen, Q., Jiang, D., & Delgrossi, L. (2009). IEEE 1609.4 DSRC Multi-Channel Operations and Its Implications on Vehicle Safety Communications. In Vehicular Networking Conference (VNC), 2009 IEEE (pp. 1-8)). Also, simTD (for reference, see H. Stubing, M. Bechler, D. Heussner, T. May, I. Radusch, H. Rechner, and P. Vogel: “sim td: a car-to-x system architecture for field operational tests [topics in automotive networking]”, in IEEE Communications Magazine, vol. 48, no. 5, pp. 148-154, 2010), one of the major field trials for inter-vehicular communication, has developed architecture and message formats for MCO.
The design of a MCO solution is challenging due to the characteristics of VANETs: Their applications have specific requirements with distinct requirements, particularly for latency and reliability, which MCO must provide support. Furthermore, the decentralized organization of VANETS and their dynamic and ephemeral characteristics creates challenges in protocol design, where nodes only have local information available for decision making. MCO can be enabled by single or dual-radio transceivers. Although the initial release of inter-vehicular communication systems is based on single-radio transceiver, it is foreseen that the next generations rely on dual-radio transceiver settings for improved performance.